A method for determining ion concentration based on a double electrolytic cell ion selective electrode

Abstract

The application relates to the field of electrochemistry, in particular to a method for determining ion concentration based on a double electrolytic cell ion selective electrode, which comprises the following steps: using a poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) modified glassy carbon electrode or a reduced graphene oxide modified glassy carbon electrode as a working electrode, using a full solid-state ion selective electrode as a reference electrode, and using a platinum wire electrode as a counter electrode; inserting the working electrode and the counter electrode into a test electrolytic cell, inserting the reference electrode into a sample electrolytic cell, connecting the test electrolytic cell and the sample electrolytic cell through Ag / AgCl as a salt bridge, and determining the ion concentration in a to-be-measured solution by adopting a constant potential coulomb analysis method. The technical scheme of the application can minimize the current response time while ensuring the accuracy of ion concentration determination, realizes rapid measurement of ion concentration, and can be applied to detection of ion concentration in human serum.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemistry, and in particular to a method for determining ion concentration based on a double electrolytic cell. BACKGROUND

[0002] Ion selective electrode (ISE) is an electrochemical sensor that measures the activity or concentration of ions in solution using membrane potential. It has the ability to detect the concentration of K + , Li + , Na + , Mg 2+ , Ca 2+ , Pb 2+ , NH4 + , CO3 2- , NO3 - , Cl - , etc. and is widely used in clinical diagnosis, blood testing, environmental testing, industrial process analysis, agriculture and food industry, etc.

[0003] Potentiometric analysis is the main testing method of ion selective electrode. The test solution is used as the electrolyte solution of the chemical cell, and two electrodes are inserted into it. One is the ion selective electrode (usually negative) whose potential changes with the activity (or concentration) of the measured ion in the test solution, and the other is the reference electrode (usually positive) whose potential remains basically unchanged with the activity (or concentration) of the measured ion in the test solution. By measuring the electromotive force of the cell, the content of the measured ion is determined according to the quantitative relationship between the electromotive force and the activity (or concentration) of the measured ion (Nernst equation). Potentiometric analysis has the advantages of good selectivity, simple equipment, and easy operation, but its limitations are poor potential reproducibility and limited measurement sensitivity by Nernst equation. That is, a potential difference of 1 mV means a 4% change in the activity (or concentration) of monovalent ions, and an 8% change in the activity (or concentration) of divalent ions. In clinical diagnosis and treatment, the sensitivity of the detection method is particularly important for samples with narrow activity (or concentration) range.

[0004] In recent years, the coulometric analysis method gradually attracts people's attention, unlike the potential analysis method, the coulometric analysis method is based on measuring the electric quantity consumed by the measured substance directly or indirectly on the electrode in the electrolysis process, in the electrolysis process, the amount of substance reacted on the electrode is proportional to the electric quantity through the electrolytic cell, under appropriate conditions, the cumulative electric quantity through the electrolytic cell is measured, and the content of the measured substance can be calculated according to Faraday's law, although the sensitivity of the coulometric analysis method is higher, and the concentration change of 0.1% can be tested, but due to the long current response time, the measurement is unstable, thereby limiting the further application of the coulometric analysis method. SUMMARY

[0005] The first object of the present application is to provide a method for measuring ion concentration based on a double electrolytic cell ion selective electrode, which is simple in operation, high in sensitivity, can minimize the current response time while ensuring the accuracy of ion concentration measurement, realizes the rapid measurement of ion concentration, and can be applied to the detection of ion concentration in human serum.

[0006] The present application provides a method for measuring ion concentration based on a double electrolytic cell ion selective electrode, comprising the following steps:

[0007] a. poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) modified glassy carbon electrode or reduced graphene oxide modified glassy carbon electrode is used as the working electrode, a full solid ion selective electrode is used as the reference electrode, and a platinum wire electrode is used as the counter electrode;

[0008] b. electrolyte solution is added to the test electrolytic cell, the measured solution is added to the sample electrolytic cell, and Ag / AgCl is used as the salt bridge to connect the test electrolytic cell and the sample electrolytic cell;

[0009] c. the working electrode and the counter electrode are inserted into the test electrolytic cell, the reference electrode is inserted into the sample electrolytic cell, and the constant potential coulometric analysis method is used to measure the ion concentration in the measured solution.

[0010] By placing the all-solid-state ion selective electrode as a reference electrode in the sample electrolytic cell, the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) modified glassy carbon electrode or the reduced graphene oxide modified glassy carbon electrode as a working electrode in the test electrolytic cell, and using Ag / AgCl as a salt bridge to connect the test electrolytic cell and the sample electrolytic cell, when the ion concentration of the solution to be measured in the sample electrolytic cell changes, the all-solid-state ion selective electrode as a reference electrode also changes, and since the potential between the working electrode and the reference electrode remains constant, the potential change of the all-solid-state ion selective electrode will cause the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) or the reduced graphene oxide on the working electrode to undergo oxidation / reduction (charging / discharging) to compensate for the potential change of the all-solid-state ion selective electrode, and the electric quantity obtained by integrating the current with respect to time is used as an analysis signal to calculate the ion concentration in the solution to be measured.

[0011] In addition, since the signal of the traditional electrolytic cell is derived from the all-solid-state ion selective electrode, but the coulomb transduction signal on the all-solid-state ion selective electrode is affected by the high impedance of the ion film, resulting in slow current response speed and limited ion analysis signal amplification, and the present application uses a double electrolytic cell to place the working electrode and the reference electrode in the test electrolytic cell and the sample electrolytic cell, respectively, and the current and the electric quantity are derived from the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) or the reduced graphene oxide in the working electrode, and no current passes through the all-solid-state ion selective electrode as a reference electrode, which can reduce the polarization interference of the all-solid-state ion selective electrode, amplify the ion analysis signal, effectively shorten the current response time, and realize rapid determination of the ion concentration.

[0012] Preferably, the preparation method of the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) modified glassy carbon electrode comprises the following steps:

[0013] S1. Polishing the glassy carbon electrode, ultrasonic cleaning the polished glassy carbon electrode and drying it for standby;

[0014] S2. Loading poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) on the surface of the glassy carbon electrode by electrochemical deposition, and after deposition, cleaning and drying to obtain a poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) modified glassy carbon electrode.

[0015] Preferably, in step S2, the process conditions of electrochemical deposition are as follows: the deposition current is 0.014 mA, the density of the deposition current is 0.2 mA / cm2, the deposition time is 70-1400 s, and the deposition electric quantity is 1-20 mC.

[0016] Preferably, the preparation method of the reduced graphene oxide modified glassy carbon electrode comprises the following steps:

[0017] (1) polishing the glassy carbon electrode, ultrasonic cleaning and drying the polished glassy carbon electrode, and reserving for use;

[0018] (2) dialysis treatment of graphene oxide to obtain an aqueous graphene oxide solution, hydrothermal reaction of the aqueous graphene oxide solution, filtration, washing and vacuum drying after the reaction to obtain reduced graphene oxide;

[0019] (3) uniformly mixing Nafion solution and N-methyl pyrrolidone to obtain a mixed solution, uniformly mixing the reduced graphene oxide and the mixed solution to obtain a reduced graphene oxide solution;

[0020] (4) drop coating the reduced graphene oxide solution on the surface of the glassy carbon electrode, and drying to obtain a reduced graphene oxide modified glassy carbon electrode.

[0021] The glassy carbon electrode is modified by poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) or reduced graphene oxide, the oxidation / reduction reaction of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) or reduced graphene oxide is used to supplement the potential change of the all-solid-state ion selective electrode, and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) or reduced graphene oxide has high stability and fast electron shuttle capability, thereby further reducing the response time and improving the accuracy of ion concentration testing.

[0022] Preferably, the polishing is performed twice, the first polishing uses Al2O3 powder with a particle size of 0.3 μm, the second polishing uses Al2O3 powder with a particle size of 0.05 μm, and water and ethanol are used for ultrasonic cleaning of the glassy carbon electrode after each polishing.

[0023] Preferably, in step (2), the dialysis is performed not less than 5 times, the hydrothermal reaction is performed at a temperature of 150-170℃ for 2.5-3.5 h, the washing is performed 5-6 times, and the vacuum drying is performed at a temperature of 55-65℃.

[0024] The dialysis treatment of graphene oxide is used to remove impurities or inorganic ions present in the graphene oxide.

[0025] Preferably, in step (3), the concentration of the reduced graphene oxide solution is 10 mg / mL, and the volume ratio of the Nafion solution to N-methyl pyrrolidone is 1:4.

[0026] In step (4), the volume of the reduced graphene oxide solution is 4-15 μL, and the drying temperature is 55-65℃.

[0027] Preferably, the all-solid-state ion-selective electrode is selected from one of all-solid-state potassium ion-selective electrode, all-solid-state sodium ion-selective electrode, all-solid-state hydrogen ion-selective electrode, all-solid-state nitrate ion-selective electrode, and all-solid-state calcium ion-selective electrode.

[0028] Preferably, the method for preparing the all-solid-state potassium ion-selective electrode comprises the following steps:

[0029] ① Valinomycin, potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, tetra(4-chlorophenyl)borate dodecylammonium, dioctyl sebacate, and polyvinyl chloride are dissolved in tetrahydrofuran to obtain a potassium ion-selective membrane solution;

[0030] ② The potassium ion-selective membrane solution is drop-coated on a poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) modified glassy carbon electrode or a graphene oxide modified glassy carbon electrode, and dried to obtain the all-solid-state potassium ion-selective electrode.

[0031] Preferably, the mass ratio of the solute to tetrahydrofuran is 1:6.67.

[0032] In the solute, the mass percentage of valinomycin is 1wt%, the mass percentage of potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate is 0.5wt%, the mass percentage of tetra(4-chlorophenyl)borate dodecylammonium is 1wt%, the mass percentage of dioctyl sebacate is 65.3wt%, and the mass percentage of polyvinyl chloride is 32.2wt%.

[0033] The present application has the following advantages:

[0034] (1) The technical scheme of the present application can amplify the ion analysis signal, reduce the current response time to the maximum, ensure the accuracy of ion concentration determination, realize the rapid measurement of ion concentration, and can be applied to the detection of ion concentration in human serum, by constructing a double electrolytic cell and using poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) or reduced graphene oxide as a novel solid-state transduction layer of the all-solid-state ion-selective electrode.

[0035] (2) The technical scheme of the present application can reduce the polarization interference of the all-solid-state ion-selective electrode, effectively shorten the current response time, and realize the rapid determination of ion concentration, by placing the working electrode and the reference electrode in the test electrolytic cell and the sample electrolytic cell respectively, and the current and the electric quantity are derived from the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) or reduced graphene oxide in the working electrode, and no current passes through the all-solid-state ion-selective electrode as the reference electrode.

[0036] (3) The technical scheme of the present application adopts poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) or reduced graphene oxide as a novel solid-state transduction layer of a full-solid-state ion-selective electrode, which has high stability and fast electron shuttling capability, thereby further reducing the response time and improving the accuracy of ion concentration testing. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to more clearly illustrate the specific embodiments of the present application or the technical schemes in the prior art, the drawings needed in the specific embodiments or prior art description will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0038] Figure 1 It is a structural schematic diagram of the double electrolytic cell in Example 1 of the present application.

[0039] Figure 2 It is a potentiometric calibration diagram of the full-solid-state potassium ion-selective electrode in Example 1 of the present application.

[0040] Figure 3 It is a coulombic transduction signal diagram of the double electrolytic cell in Example 1 of the present application.

[0041] Figure 4 It is a cyclic back-and-forth diagram of the coulombic response of the double electrolytic cell in Example 1 of the present application.

[0042] Figure 5 It is a diagram of the relationship between the cumulative charge of the double electrolytic cell and Log a K+ in Examples 1-4 of the present application.

[0043] Figure 6 It is a linear diagram of the linear slope of the cumulative charge of the double electrolytic cell relative to Log a K+ and the low-frequency impedance capacitance in Examples 1-4 of the present application.

[0044] Figure 7 It is a diagram of the relationship between the chronoamperometric response cumulative charge of the double electrolytic cell and time in Example 1 of the present application.

[0045] Figure 8 It is a diagram of the relationship between the chronoamperometric response cumulative charge of the double electrolytic cell and Log a K+ in Example 1 of the present application.

[0046] Figure 9 It is a coulombic transduction signal diagram of the single electrolytic cell in Comparative Example 1 of the present application.

[0047] 1-Test electrolytic cell, 2-Sample electrolytic cell, 3-Reference electrode, 4-Counter electrode, 5-Working electrode, 6-Salt bridge. Detailed Implementation

[0048] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0050] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. Furthermore, the terms "installed," "connected," and "linked" should be interpreted broadly; for example, they may refer to a fixed connection, a detachable connection, or an integral connection; they may refer to a mechanical connection or an electrical connection; they may refer to a direct connection or an indirect connection through an intermediate medium; and they may refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0051] Example 1

[0052] Depend on Figure 1 As shown, an apparatus for determining ion concentration based on a dual-electrolysis cell ion-selective electrode includes a test electrolysis cell 1, which is connected to a sample electrolysis cell 2 via a salt bridge 6. A working electrode 5 and a counter electrode 4 are inserted inside the test electrolysis cell 1 and are connected to each other. A reference electrode 3 is inserted inside the sample electrolysis cell 2 and is connected to the working electrode 5 and the counter electrode 4, respectively.

[0053] The working electrode 5 is a reduced graphene oxide modified glassy carbon electrode, the reference electrode 3 is a full solid-state potassium ion selective electrode, the counter electrode 4 is a platinum wire electrode, and the salt bridge 6 is Ag / AgCl.

[0054] A method for determining ion concentration based on a double electrolytic cell ion selective electrode, comprising the following steps:

[0055] S1. Select a glassy carbon electrode with a diameter of 3mm, perform first polishing treatment on the glassy carbon electrode with 0.3μm Al2O3 powder on a nylon cloth, ultrasonic clean the polished glassy carbon electrode with water and ethanol in sequence, then perform second polishing treatment on the glassy carbon electrode with 0.05μm Al2O3 powder on a nylon cloth, ultrasonic clean the polished glassy carbon electrode with water and ethanol in sequence, dry and reserve;

[0056] S2. Perform 5 times of dialysis treatment on graphene oxide to remove impurities or inorganic ions existing in the graphene oxide, obtain graphene oxide aqueous solution, perform hydrothermal reaction on the graphene oxide aqueous solution at 150℃ for 2.5h, after the reaction is completed, cool to room temperature, filter, wash with deionized water for 5 times, and vacuum dry at 55℃ to obtain reduced graphene oxide;

[0057] S3. Mix 20μL Nafion solution and 80μL N-methylpyrrolidone uniformly to obtain a mixed solution, mix 10mg reduced graphene oxide with the mixed solution uniformly to obtain a reduced graphene oxide solution with a concentration of 10mg / mL;

[0058] S4. Take 6μL reduced graphene oxide solution and drop coat on the surface of the glassy carbon electrode, dry at 55℃ to obtain a reduced graphene oxide modified glassy carbon electrode.

[0059] S5. Dissolve 1wt% valinomycin, 0.5wt% potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, 1wt% tetra(4-chlorophenyl)borate dodecylammonium, 65.3wt% dioctyl sebacate and 32.2wt% polyvinyl chloride as solutes in tetrahydrofuran to obtain a potassium ion selective membrane solution, and the mass ratio of the solutes to tetrahydrofuran is 1:6.67;

[0060] S6. Drop coat 50μL potassium ion selective membrane solution on the reduced graphene oxide modified glassy carbon electrode, dry at 55℃ to obtain a full solid-state potassium ion selective electrode;

[0061] S7. Add 0.1mol / L KCl into the test electrolytic cell 1, add the solution to be tested into the sample electrolytic cell 2, and connect the test electrolytic cell 1 and the sample electrolytic cell 2 with Ag / AgCl as the salt bridge 6;

[0062] S8. Take the reduced graphene oxide modified glassy carbon electrode as the working electrode 4, the platinum wire electrode as the counter electrode 5, and the full solid-state potassium ion selective electrode as the reference electrode 3, insert the working electrode 4 and the counter electrode 5 into the test electrolytic cell 1, and insert the reference electrode 3 into the sample electrolytic cell 2, and then determine the ion concentration in the to-be-measured solution by using the constant potential coulomb analysis method.

[0063] Example 2

[0064] A method for determining ion concentration by using a double electrolytic cell based ion selective electrode, comprising the following steps:

[0065] S1. Select a glassy carbon electrode with a diameter of 5 mm, perform first polishing treatment on the glassy carbon electrode with 0.3 μm Al2O3 powder on a nylon cloth, ultrasonic clean the polished glassy carbon electrode with water and ethanol in sequence, then perform second polishing treatment on the glassy carbon electrode with 0.05 μm Al2O3 powder on a nylon cloth, ultrasonic clean the polished glassy carbon electrode with water and ethanol in sequence, and dry the glassy carbon electrode for standby use;

[0066] S2. Connect the glassy carbon electrode and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) by using a CHI 1030C electrochemical workstation, deposit 70 s by applying a constant current of 0.014 mA, so as to load the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) on the surface of the glassy carbon electrode, the current density is 0.2 mA / cm 2 , the deposition amount is 1 mC, after the deposition is completed, rinse with deionized water, and dry at room temperature to obtain a poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) modified glassy carbon electrode;

[0067] S3. Dissolve 1 wt% valinomycin, 0.5 wt% potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, 1 wt% tetra(4-chlorophenyl)borate dodecylammonium, 65.3 wt% dioctyl sebacate, and 32.2 wt% polyvinyl chloride as solutes in tetrahydrofuran to obtain a potassium ion selective membrane solution, and the mass ratio of the solutes to tetrahydrofuran is 1:6.67;

[0068] S6. Drop coat 50 μL of the potassium ion selective membrane solution on the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) modified glassy carbon electrode, and dry at 55°C to obtain a full solid-state potassium ion selective electrode;

[0069] S7. Add 0.1 mol / L KCl into the test electrolytic cell 1, add the to-be-measured solution into the sample electrolytic cell 2, and connect the test electrolytic cell 1 and the sample electrolytic cell 2 by using Ag / AgCl as a salt bridge 6;

[0070] S8. The poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) modified glassy carbon electrode is used as the working electrode 4, the platinum wire electrode is used as the counter electrode 5, and the full solid-state potassium ion selective electrode is used as the reference electrode 3. The working electrode 4 and the counter electrode 5 are inserted into the test electrolytic cell 1, and the reference electrode 3 is inserted into the sample electrolytic cell 2. The ion concentration in the solution to be measured is determined by the constant potential coulometric analysis method.

[0071] Example 3

[0072] A method for determining ion concentration based on a double electrolytic cell ion selective electrode, comprising the following steps:

[0073] S1. A glassy carbon electrode with a diameter of 5 mm is selected. The glassy carbon electrode is first polished on a nylon cloth with 0.3 μm Al2O3 powder, and then ultrasonically cleaned with water and ethanol. Next, the glassy carbon electrode is second polished on a nylon cloth with 0.05 μm Al2O3 powder, and then ultrasonically cleaned with water and ethanol. After drying, the glassy carbon electrode is ready for use.

[0074] S2. The CHI 1030C electrochemical workstation is used to connect the glassy carbon electrode and the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid). A constant current of 0.014 mA is applied for 350 s to deposit the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) on the surface of the glassy carbon electrode. The current density is 0.2 mA / cm 2 , and the deposition charge is 5 mC. After deposition, the glassy carbon electrode is rinsed with deionized water and dried at room temperature to obtain a poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) modified glassy carbon electrode.

[0075] S3. 1 wt% valinomycin, 0.5 wt% potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, 1 wt% tetra(4-chlorophenyl)borate dodecylammonium, 65.3 wt% dioctyl sebacate, and 32.2 wt% polyvinyl chloride are dissolved in tetrahydrofuran as solutes to obtain a potassium ion selective membrane solution. The mass ratio of the solutes to tetrahydrofuran is 1:6.67.

[0076] S6. 50 μL of the potassium ion selective membrane solution is dropped on the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) modified glassy carbon electrode and dried at 60°C to obtain a full solid-state potassium ion selective electrode.

[0077] S7. 0.1 mol / L KCl is added to the test electrolytic cell 1, and the solution to be measured is added to the sample electrolytic cell 2. The Ag / AgCl salt bridge 6 is used to connect the test electrolytic cell 1 and the sample electrolytic cell 2.

[0078] S8. The poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) modified glassy carbon electrode is used as the working electrode 4, the platinum wire electrode is used as the counter electrode 5, and the full solid-state potassium ion selective electrode is used as the reference electrode 3. The working electrode 4 and the counter electrode 5 are inserted into the test electrolytic cell 1, and the reference electrode 3 is inserted into the sample electrolytic cell 2. The ion concentration in the solution to be measured is determined by the constant potential coulometric analysis method.

[0079] Example 4

[0080] A method for determining ion concentration based on a double electrolytic cell ion selective electrode, comprising the following steps:

[0081] S1. A glassy carbon electrode with a diameter of 3 mm is selected. The glassy carbon electrode is first polished on a nylon cloth with 0.3 μm Al2O3 powder, and then ultrasonically cleaned with water and ethanol. Next, the glassy carbon electrode is second polished on a nylon cloth with 0.05 μm Al2O3 powder, and then ultrasonically cleaned with water and ethanol. After drying, the glassy carbon electrode is ready for use.

[0082] S2. The CHI 1030C electrochemical workstation is used to connect the glassy carbon electrode and the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid). A constant current of 0.014 mA is applied for 1400 s to deposit the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) on the surface of the glassy carbon electrode. The current density is 0.2 mA / cm 2 , and the deposition charge is 20 mC. After deposition, the glassy carbon electrode is rinsed with deionized water and dried at room temperature to obtain a poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) modified glassy carbon electrode.

[0083] S3. 1 wt% valinomycin, 0.5 wt% potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, 1 wt% tetra(4-chlorophenyl)borate dodecylammonium, 65.3 wt% dioctyl sebacate, and 32.2 wt% polyvinyl chloride are dissolved in tetrahydrofuran as solutes to obtain a potassium ion selective membrane solution. The mass ratio of the solutes to tetrahydrofuran is 1:6.67.

[0084] S6. 50 μL of the potassium ion selective membrane solution is dropped on the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) modified glassy carbon electrode and dried at 65°C to obtain a full solid-state potassium ion selective electrode.

[0085] S7. 0.1 mol / L KCl is added to the test electrolytic cell 1, and the solution to be measured is added to the sample electrolytic cell 2. The Ag / AgCl salt bridge 6 is used to connect the test electrolytic cell 1 and the sample electrolytic cell 2.

[0086] S8. The poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) modified glassy carbon electrode is used as the working electrode 4, the platinum wire electrode is used as the counter electrode 5, and the full solid-state potassium ion selective electrode is used as the reference electrode 3. The working electrode 4 and the counter electrode 5 are inserted into the test electrolytic cell 1, and the reference electrode 3 is inserted into the sample electrolytic cell 2. The ion concentration in the solution to be measured is determined by the constant potential coulomb analysis method.

[0087] Example 4

[0088] A method for determining ion concentration based on a double electrolytic cell ion selective electrode, comprising the following steps:

[0089] S1. A glassy carbon electrode with a diameter of 3 mm is selected. The glassy carbon electrode is first polished on a nylon cloth with 0.3 μm Al2O3 powder, and then ultrasonically cleaned with water and ethanol. Next, the glassy carbon electrode is second polished on a nylon cloth with 0.05 μm Al2O3 powder, and then ultrasonically cleaned with water and ethanol. After drying, the glassy carbon electrode is ready for use.

[0090] S2. The graphene oxide is dialyzed for 7 times to remove impurities or inorganic ions present in the graphene oxide, and an aqueous graphene oxide solution is obtained. The aqueous graphene oxide solution is subjected to hydrothermal reaction at 160℃ for 3.0 h. After the reaction is completed, the solution is cooled to room temperature, filtered, washed with deionized water for 6 times, and dried under vacuum at 60℃ to obtain reduced graphene oxide.

[0091] S3. 20 μL of Nafion solution and 80 μL of N-methylpyrrolidone are uniformly mixed to obtain a mixed solution. 10 mg of reduced graphene oxide is uniformly mixed with the mixed solution to obtain a reduced graphene oxide solution with a concentration of 10 mg / mL.

[0092] S4. 10 μL of the reduced graphene oxide solution is drop-coated on the surface of the glassy carbon electrode, and the glassy carbon electrode modified with reduced graphene oxide is obtained after drying at 60℃.

[0093] S5. 1 wt% valinomycin, 0.5 wt% potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, 1 wt% tetra(4-chlorophenyl)borate dodecylammonium, 65.3 wt% dioctyl sebacate, and 32.2 wt% polyvinyl chloride are dissolved in tetrahydrofuran as solutes to obtain a potassium ion selective membrane solution, and the mass ratio of the solutes to tetrahydrofuran is 1:6.67.

[0094] S6. 50 μL of the potassium ion selective membrane solution is drop-coated on the glassy carbon electrode modified with reduced graphene oxide, and the full solid-state potassium ion selective electrode is obtained after drying at 60℃.

[0095] S7. 0.1 mol / L KCl is added into the test electrolytic cell 1, and the solution to be measured is added into the sample electrolytic cell 2, and the Ag / AgCl is used as the salt bridge 6 to connect the test electrolytic cell 1 and the sample electrolytic cell 2;

[0096] S8. The reduced graphene oxide modified glassy carbon electrode is used as the working electrode 4, the platinum wire electrode is used as the counter electrode 5, and the all-solid-state potassium ion selective electrode is used as the reference electrode 3, the working electrode 4 and the counter electrode 5 are inserted into the test electrolytic cell 1, and the reference electrode 3 is inserted into the sample electrolytic cell 2, and the ion concentration in the solution to be measured is determined by using the constant potential coulomb analysis method.

[0097] Example 6

[0098] A method for determining ion concentration based on a double electrolytic cell ion selective electrode, comprising the following steps:

[0099] S1. A glassy carbon electrode with a diameter of 5 mm is selected, the glassy carbon electrode is subjected to a first polishing treatment on a nylon cloth by using 0.3 μm Al2O3 powder, the polished glassy carbon electrode is ultrasonically cleaned with water and ethanol in sequence, then the glassy carbon electrode is subjected to a second polishing treatment on a nylon cloth by using 0.05 μm Al2O3 powder, the polished glassy carbon electrode is ultrasonically cleaned with water and ethanol in sequence, and after drying, the glassy carbon electrode is ready for use;

[0100] S2. The graphene oxide is subjected to 10 times of dialysis treatment to remove impurities or inorganic ions existing in the graphene oxide, and an aqueous graphene oxide solution is obtained, the aqueous graphene oxide solution is subjected to hydrothermal reaction at 165℃ for 3.5 h, after the reaction is completed, the solution is cooled to room temperature, filtered, washed with deionized water for 6 times, and after vacuum drying at 65℃, reduced graphene oxide is obtained;

[0101] S3. 20 μL of Nafion solution and 80 μL of N-methylpyrrolidone are uniformly mixed to obtain a mixed solution, 10 mg of reduced graphene oxide is uniformly mixed with the mixed solution to obtain a reduced graphene oxide solution with a concentration of 10 mg / mL;

[0102] S4. 15 μL of the reduced graphene oxide solution is drop-coated on the surface of the glassy carbon electrode, and after drying at 65℃, a reduced graphene oxide modified glassy carbon electrode is obtained.

[0103] S5. 1 wt% valinomycin, 0.5 wt% potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, 1 wt% tetra(4-chlorophenyl)borate dodecylammonium, 65.3 wt% dioctyl sebacate, and 32.2 wt% polyvinyl chloride are dissolved in tetrahydrofuran as solutes to obtain a potassium ion selective membrane solution, and the mass ratio of the solutes to tetrahydrofuran is 1:6.67;

[0104] S6. Drop-coat 50 μL of potassium ion selective membrane solution onto a glassy carbon electrode modified with reduced graphene oxide and dry it at 65 °C to obtain an all-solid-state potassium ion selective electrode;

[0105] S7. Add 0.1 mol / L KCl to test electrolytic cell 1, add the test solution to sample electrolytic cell 2, and connect test electrolytic cell 1 and sample electrolytic cell 2 with Ag / AgCl as salt bridge 6.

[0106] S8. Using a glassy carbon electrode modified with reduced graphene oxide as the working electrode 4, a platinum wire electrode as the counter electrode 5, and an all-solid-state potassium ion selective electrode as the reference electrode 3, the working electrode 4 and the counter electrode 5 are inserted into the test electrolytic cell 1, and the reference electrode 3 is inserted into the sample electrolytic cell 2. The ion concentration in the test solution is determined by potentiostatic coulometric analysis.

[0107] Comparative Example 1

[0108] The graphene oxide-modified glassy carbon electrode prepared in Example 1 was used as the working electrode, the platinum wire electrode as the counter electrode, and the all-solid-state potassium ion selective electrode prepared in Example 1 as the reference electrode. The working electrode, counter electrode, and reference electrode were inserted into the test electrolytic cell.

[0109] Test case

[0110] (1) Potential calibration of all-solid-state potassium ion selective electrode

[0111] Before measurement, the all-solid-state potassium ion-selective electrode was calibrated using a 16-channel potentiometer. Figure 2 As shown, the calibration slope of the all-solid-state potassium ion selective electrode is 57±2mV / decade.

[0112] (2) Response time and sensitivity

[0113] Using 5 ml of 5 mmol / L KNO3 as the starting solution and 0.1 mol / L NaCl as the starting solution as the constant background ion solution, 5 μl of 0.01 mol / L KNO3 was added sequentially to the starting solution, with an interval of approximately 15-20 seconds between each addition. The response time and sensitivity of the coulometric transduction method in the dual electrolytic cell of Example 1 and the single electrolytic cell of Comparative Example 1 were tested using a CHI1030C electrochemical workstation and the galvanostatic method.

[0114] Depend on Figure 3 As shown, a is the chronoamperometry diagram of the dual electrolytic cell, b is an enlarged chronoamperometry diagram of the dilution process of a single solution, c is the relationship between the cumulative charge and time in the dual electrolytic cell, and d is the relationship between the cumulative charge and K in the dual electrolytic cell. + The graph showing the relationship between concentrations, starting with an initial solution of 0.01 mol / L KNO3, with each increment Δlog a...K+ With an activity change of 0.3, the current measurement response time of the dual electrolytic cell is only 5s, and the current response can reach 35μA. Figure 3 b) The cumulative charge curve of the dual electrolytic cells shows a stepped shape. Figure 3 c) indicates that the dual electrolytic cell reaches complete equilibrium within a short time interval. Furthermore, the cumulative charge in each dilution step of the dual electrolytic cell is 25 μC. Figure 3 d).

[0115] Depend on Figure 9 As shown, a is a chronoamperometry diagram of a single electrolytic cell, b is an enlarged chronoamperometry diagram of a single solution dilution process, c is a graph showing the relationship between the cumulative charge and time in a single electrolytic cell, and d is a graph showing the relationship between the cumulative charge and K in a single electrolytic cell. + The graph showing the logarithm relationship between concentrations, starting with the same initial solution of 0.01 mol / L KNO3, with each increment Δlog a... K+ With an activity change of 0.3, the current response time of a single electrolytic cell is 5 minutes, and the current response can reach 25 nA. Figure 9 b) The equilibrium time of a single electrolytic cell is 5 minutes, which is significantly longer than that of a dual electrolytic cell. Figure 9 c), in addition, the cumulative charge per dilution step in a single electrolytic cell is 1.5 μC ( Figure 9 d).

[0116] As can be seen from the above, in a single electrolytic cell system, if the time response is too long, the instability of the potential will lead to the drift of the current baseline, which in turn affects the stability of the accumulated charge signal. This invention constructs a dual electrolytic cell system, which amplifies the ion analysis signal by amplifying the capacitance or charge on the surface of the modified working electrode, thereby shortening the current response time. In the dual electrolytic cell system, the current measurement response only takes 5 seconds, and compared with the single electrolytic cell system, the dual electrolytic cell system can reach equilibrium within a short time interval. In addition, under the same conditions, the accumulated charge in each dilution step of the dual electrolytic cell system is about 16 times that of the single electrolytic cell system, and the linear regression of charge in the dual electrolytic cell system is significantly better than that in the single electrolytic cell system.

[0117] (3) Cyclic response of the dual electrolytic cell

[0118] Depend on Figure 4 As shown, when K + When the concentration varied between 0.5 mmol / L and 1 mmol / L, the current and charge responses driven by the potential change of the all-solid-state potassium ion-selective electrode showed reversibility. When the all-solid-state potassium ion-selective electrode was used as the reference electrode and the reduced graphene oxide-modified glassy carbon electrode was used as the working electrode, K... +When the concentration changes from 1 mmol / L to 0.5 mmol / L, the current response can reach 60 mA, the required equilibrium time is less than 10 s, and the cumulative charge Q is about 170 μC, which is 85 times higher than that of the single electrolytic cell coulometric method (about 2 μC) under the same conditions.

[0119] (4) Accumulated electricity and relative to K + linearity of the logarithm of concentration

[0120] Depend on Figure 5 As shown, when glassy carbon electrodes modified with 1mC or 20mC poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) or 6μL or 10μL reduced graphene oxide are used as working electrodes, the cumulative charge is in the range of -2.0 to -3.2 K. + The logarithmic change in concentration is linearly proportional, and the cumulative charge of the coulomb signal is amplified as the capacitance of the solid transconductance layer on the working electrode surface increases.

[0121] And by Figure 6 As shown, the linear slope of the cumulative charge with respect to ion activity increases linearly with the capacitance obtained from the low-frequency impedance. As can be seen from the above, the larger the capacitance or charge of the solid transconductance layer on the working electrode, the larger the charge in the coulometric method. The slope can be amplified by applying a larger capacitance to obtain better sensitivity.

[0122] (5) K of the coulometric method in a dual electrolytic cell + Sensitivity test

[0123] The effect of the dual electrolytic cell on K in Example 1 was tested using the constant current method. + The sensitivity of the detection is obtained by integrating the current over time, thus yielding the curve of the cumulative charge changing over time. Figure 7 As shown, the minimum concentration difference between the two points is 0.2%, indicating that the coulometric response of the dual-electrolysis cell has significant sensitivity. Furthermore, within a small range of concentration changes, the cumulative charge curve and K... + The logarithm of concentration shows a linear relationship, such as... Figure 8 As shown.

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining ion concentration using an ion-selective electrode based on a dual-electrolysis cell, characterized in that, Includes the following steps: a. A glassy carbon electrode modified with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) or a glassy carbon electrode modified with reduced graphene oxide is used as the working electrode, an all-solid-state ion-selective electrode is used as the reference electrode, and a platinum wire electrode is used as the counter electrode. b. Add the electrolyte solution to the test electrolytic cell and the solution to be tested to the sample electrolytic cell, and connect the test electrolytic cell and the sample electrolytic cell with Ag / AgCl as a salt bridge; c. Insert the working electrode and counter electrode into the test electrolytic cell, and the reference electrode into the sample electrolytic cell. Use potentiostatic coulometric analysis to determine the ion concentration in the test solution.

2. The method for determining ion concentration using an ion-selective electrode based on a dual-electrolysis cell according to claim 1, characterized in that, A method for preparing a poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) modified glassy carbon electrode includes the following steps: S1. Polish the glassy carbon electrode, then ultrasonically clean and dry the polished glassy carbon electrode for later use; S2. Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) was loaded onto the surface of a glassy carbon electrode by electrochemical deposition. After deposition, the electrode was cleaned and dried to obtain a glassy carbon electrode modified with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid).

3. The method for determining ion concentration using an ion-selective electrode based on a dual electrolytic cell according to claim 2, characterized in that, In step S2, the electrochemical deposition process conditions are as follows: deposition current is 0.014 mA, and deposition current density is 0.2 mA / cm³. 2 The deposition time is 70-1400s, and the deposition charge is 1-20mC.

4. The method for determining ion concentration using an ion-selective electrode based on a dual electrolytic cell according to claim 1, characterized in that, A method for preparing a glassy carbon electrode modified with reduced graphene oxide includes the following steps: (1) Polish the glassy carbon electrode, then ultrasonically clean and dry the polished glassy carbon electrode for later use; (2) Dialyze the graphene oxide to obtain an aqueous solution of graphene oxide. Then, subject the aqueous solution of graphene oxide to a hydrothermal reaction. After the reaction is completed, filter, wash, and vacuum dry to obtain reduced graphene oxide. (3) Mix Nafion solution and N-methylpyrrolidone evenly to obtain a mixture, and then mix the reduced graphene oxide with the mixture evenly to obtain a reduced graphene oxide solution. (4) Take the reduced graphene oxide solution and drop it onto the surface of the glassy carbon electrode. After drying, the glassy carbon electrode modified with reduced graphene oxide is obtained.

5. The method for determining ion concentration using an ion-selective electrode based on a dual-electrolysis cell according to claim 2 or 4, characterized in that, The polishing process was repeated twice. For the first polishing, Al2O3 powder with a particle size of 0.3 μm was used, and for the second polishing, Al2O3 powder with a particle size of 0.05 μm was used. After each polishing, the glassy carbon electrode was ultrasonically cleaned with water and ethanol in sequence.

6. The method for determining ion concentration using an ion-selective electrode based on a dual electrolytic cell according to claim 4, characterized in that, In step (2), the number of dialysis cycles is no less than 5, the temperature of the hydrothermal reaction is 150-170℃, the time of the hydrothermal reaction is 2.5-3.5h, the number of washing cycles is 5-6, and the temperature of vacuum drying is 55-65℃.

7. The method for determining ion concentration using an ion-selective electrode based on a dual electrolytic cell according to claim 4, characterized in that, In step (3), the concentration of the reduced graphene oxide solution is 10 mg / mL, and the volume ratio of Nafion solution to N-methylpyrrolidone is 1:

4. In step (4), the volume of the reduced graphene oxide solution is 4-15 μL, and the drying temperature is 55-65℃.

8. The method for determining ion concentration using an ion-selective electrode based on a dual electrolytic cell according to claim 1, characterized in that, The all-solid-state ion-selective electrode is selected from one of the following: all-solid-state potassium ion-selective electrode, all-solid-state sodium ion-selective electrode, all-solid-state hydrogen ion-selective electrode, all-solid-state nitrate ion-selective electrode, and all-solid-state calcium ion-selective electrode.

9. The method for determining ion concentration using an ion-selective electrode based on a dual electrolytic cell according to claim 8, characterized in that, The preparation method of an all-solid-state potassium ion-selective electrode includes the following steps: ① A potassium ion-selective membrane solution was obtained by dissolving valamicin, potassium tetra[3,5-di(trifluoromethyl)phenyl]borate, tetradodecylammonium tetra(4-chlorophenyl)borate, dioctyl sebacate, and polyvinyl chloride as solutes in tetrahydrofuran. ② The potassium ion selective membrane solution is drop-coated onto a poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) modified glassy carbon electrode or a reduced graphene oxide modified glassy carbon electrode, and then dried to obtain an all-solid-state potassium ion selective electrode.

10. The method for determining ion concentration using an ion-selective electrode based on a dual-electrolysis cell according to claim 9, characterized in that, The mass ratio of solute to tetrahydrofuran is 1:6.67; The solute contains 1 wt% valproic acid, 0.5 wt% potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, 1 wt% tetradodecylammonium tetrakis(4-chlorophenyl)borate, 65.3 wt% dioctyl sebacate, and 32.2 wt% polyvinyl chloride.

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